Research consistently ranks good sex as an important component of quality of life.

Back pain is a serious deal-breaker to good sex because when your back hurts, sex does too.

About 31 million people suffer from low-back pain in the US, according to the American Chiropractic Association.

From 34 to 84 percent of those people have sex less frequently, depending on what study you read.

Ergo, if you suffer from back pain—and a whole lot of people do—you’re probably having sex less and enjoying it less, as well.

That’s a lot of lost quality of life.

Now, for the first time, a group of researchers from the University of Waterloo in Canada actually studied how the back moves during sex, adding some hard data to support, and in some cases, debunk, the common advice doctors give their patients.

The first phase of this research focused on how the spine moves in a normal, healthy male during sex. To do this, lead researchers, Natalie Sidorkewicz, MSc, and Stuart McGill, M. PhD, recruited 10 heterosexual couples who did not have back pain.

Then they wired them with reflective sensors and told them to “move as naturally as possible” in five different sexual positions: two versions of the missionary position, two versions of the “doggy-style” position, and “spooning” or side-lying (the most common position recommended for people with back pain).

The researchers analyzed the data and identified the positions that were most “spine-sparing”—involving less movement—for different types of back pain.

Some people—and this is more common with age—experience back pain when they sit or bend forward. This is “flexion-intolerant” back pain. The best position for the flexion-intolerant is the quadruped or a missionary position with the male on his hands.

A second type of back pain is called “extension-intolerant,” which means that lying on the back or stomach is painful. For this type of back pain, spooning may be a better position.

For some people, any movement causes back pain, and for these “motion-intolerant” types, sex remains challenging. In general, however, movement (and pain) is lessened when it is shifted to the hip and knee, as in the quadruped position when the female is on her elbows.

With any of these positions, small adjustments—whether a person is on elbows or hands, for example—significantly changes the amount of back movement involved.

The best option for the person not controlling the movement (the females in this study) is to keep the spine in a neutral position, by supporting the small of the back with a pillow in the missionary position, for example.

A chart illustrating the best position for different types of pain is here.

Future research will focus on female back movement during sex and how the spine is affected by orgasm. The researchers also want to study the effect of various positions for actual back pain sufferers.

All this is the beginning of good news for people with back pain. Previously, medical recommendations have relied on “conjecture, clinical experience, or popular media resources,” according to the University of Waterloo study. Hard data is a welcome addition.

Researchers also hope their work will spark more dialog between patients and health care providers about sex, now that practitioners have real research to refer to in discussion with patients with back pain.